1. Field of the Invention
The present invention relates to a motor having a dynamic pressure fluid bearing and a disc drive apparatus provided with the motor.
2. Description of the Related Art
Higher reliability is required for a motor, which is utilized for a driving apparatus of a disc such as a magnetic disc so as to drive the disc rotatably. Particularly, along with increasing recording capacity of a disc, a motor having a dynamic pressure fluid bearing, which is advantageous to NRRO (Non-Repeatable Run-Out) in comparison with a bearing using a conventional ball bearing, enables to be used preferably for such a disc drive apparatus.
With respect to an example of a motor having a dynamic pressure fluid bearing (hereinafter referred to as just a motor), the Japanese Patent Application Laid-open Publication No. 10-80091/1998 discloses such a motor having a dynamic pressure fluid bearing.
The motor is composed of a shaft section and a sleeve section that is rotatable freely and relatively with respect to the shaft section. The shaft section is axially sustained by radial and thrust dynamic pressure fluid bearings.
Further, the shaft section is provided with a through hole for injecting lubrication fluid and maintaining it therein, wherein the through hole is bored through the shaft section from the top end surface to the bottom end surface.
However, in the above-mentioned motor, an amount of lubricant necessary for lubricating the dynamic pressure fluid bearing may fail to be maintained sufficiently when the amount of lubricant decreased due to exuding of the lubricant diachronically. Consequently, there existed a problem such that it was hard for life of the bearing to be maintained longer or stably.
Further, an inner wall surface of the through hole for injecting lubricant approximately intersects perpendicularly with a lower end surface of the shaft section. Therefore, in a process of manufacturing motors, when lubricant is injected into the through hole through an open hole provided in a top end portion of the through hole, air is easily led into the lubricant, and resulting in tending to remain bubbles in the lubricant.
Furthermore, in this configuration, the bubbles once let into the lubricant are blocked by a bottom end surface of the shaft section and hardly released from the lubricant to the outside of the shaft section through the through hole.
The remaining bubbles resulted in another problem such that the lubricant disabled to fulfil its performances sufficiently, and resulting in failing to ensure prescribed performances of the dynamic pressure fluid bearing, or that burning between the bearing and the shaft section easily occurred, and resulting in shortening the motor life.
Further, lubricant must be injected into the through hole so as to remain no bubble in the lubricant. Consequently, there existed a further problem such that an assembling work of motors was made difficult.